There can be marriages decades or even 200 years apart from one line to the next. I haven't been able to figure out the "logic" by which it is sorted so that I can search efficiently for specific family members. I am hoping that someone could give me some advice on how to use this index.

It's the first 100 pages especially that are confusing. I found the last names starting with Z's as you did. but I could not find the last names staring with "B" within the first 100 pages. Plus the first 20 pages are a different format, and I can't figure those out at all. After page 110, I think I have figured those out.